Motorized vehicles include a prime mover that generates input torque. The received input torque is transmitted across a hydrodynamic torque converter or a friction input clutch to an input member of the transmission. In a conventional geared transmission, the received input torque is transferred through one or more planetary gear sets by applying different combinations of friction clutches and brakes, and ultimately transmits output torque to a set of drive wheels at a selected gear ratio to propel the vehicle.
Typically, a desired park, neutral, reverse, drive, or low (PRNDL) transmission operating range is manually selected by the vehicle operator using a user interface device in the form of a floor-mounted or steering column-mounted PRNDL lever. In the drive (D) range, the transmission automatically shifts between available forward gear ratios based on speed, torque, driver requests, and other current vehicle operating conditions. The PRNDL lever is mechanically linked to a shift control valve of the transmission by a range shift mechanism consisting of a series of interconnected levers, push/pull rods, and cables. The number and size of such mechanical components can make it difficult to package the range shift mechanism between the driver interface device and the transmission, and can also add significant amounts of frictional resistance.
Several “shift-by-wire” range shift mechanisms have been developed to address such issues. Shift-by-wire range shift mechanisms are sometimes referred to as electronic transmission range selection (ETRS) systems. Typically, an ETRS system operates by toggling/command on/off states of solenoids disposed on fluid control valves and a park pawl so as to set up the hydraulics of a transmission to achieve a desired powerflow. Or, clutch pressures are commanded directly and a solenoid is toggled on a park pawl in other embodiments. A driver selects a desired range via a user input device, which may be embodied as a set of push buttons or a traditional lever in different designs. However, rather than physically actuating a shift valve via cable tension in the conventional manner, range selection in an ETRS system instead transmits a corresponding electronic range signal to a controller. The controller then commands movement of the transmission to a corresponding range select position.